This invention relates to a hollow container of biaxially oriented synthetic resin engaged with a base cap on the bottom of the container and a method of engaging the cap with the bottom of the container.
Containers of biaxially oriented synthetic resin have been recently used in a wide range of applications in great quantity. When the bottom of this container is disposed horizontally with respect to the axis of the container body as is used ordinarily in this case, the biaxial orientation of the bottom wall part of the container becomes difficult in the blow-molding step. It is preferred in order to effectively biaxially orient the bottom wall part of the container to swell the bottom wall part downwardly in a spherical shape. However, the container causes, if the bottom of the container is formed in a spherical shape, difficulty in erecting and stationarily standing the container since the bottom is spherical. To eliminate this difficulty, a base cap is engaged and disposed as a trestle for erecting and steadily standing the container in a vertical position. When an air vent is not provided at the cap, high pressure air remains between the cap and the bottom of the container due to the introduction of the bottom into the cap in case of engaging the bottom of the container within the cap, thereby causing the cap to be readily removed from the container due to the operation of the high pressure air thus produced. For the purpose, an adequate number of air vent holes are formed at the cap. When the container with the cap is, for example, submerged, after liquid is filled in the container, in chilled water to cool the filled liquid by a consumer, the chilled water is fed through the vent holes into the space between the bottom of the container and the cap, whereby water is dropped from the vent holes after the container is raised from the chilled water and cannot be dried from the water for a long period of time.
In case of engaging the container body with the base cap, the bottom of the container is mechanically press-fitted into the cap. In this case, since the press-fitting step is performed for a short time, the air in the cap loses its escaping space due to the depression of the bottom of the container into the cap, thereby frequently causing the cap to be incompletely engaged with the container.